A display device widely used in mobile phones, notebook computers, LCD monitors, flat panel TVs and the like displays images on a panel using light emitted from a backlight unit.
A backlight unit of a display device comprises a light source for emitting light, a light guide plate for allowing the light emitted from the light source to exit in the form of surface light, and at least one optical film for focusing and refracting the light exiting from the light guide plate toward a panel.
The optical film focuses and refracts the light exiting from the light guide plate to be directed toward the panel so that images having uniform luminance can be displayed on the entire region of the panel. To this end, optical patterns for focusing and refracting light are formed on a surface of the optical film. The optical film generally has a structure in which a plurality of optical patterns having a certain shape in cross section are linearly arranged at a certain pitch.
However, since such a conventional optical film has optical patterns having a certain shape in cross section and linearly arranged at a certain pitch, a moiré phenomenon may occur due to optical combination with pixel arrangement of a panel.
Meanwhile, an optical film for preventing a moiré phenomenon is disclosed in U.S. Pat. Nos. 6,354,709 and 5,919,551 and Korean Laid-open Patent Publication No 10-2007-0084410.
As shown in FIG. 1, in an optical film 1 disclosed in U.S. Pat. No. 6,354,709, a surface of the optical film is formed with optical patterns 1-1 such that peak portions thereof are non-linearly arranged. As a result, it is possible to prevent a generation of a moiré phenomenon.
As shown in FIG. 2, in an optical film 2 disclosed in U.S. Pat. No. 5,919,551, optical patterns 2-1 having irregular pitches P1, P2 and P3 are arranged on a surface of the optical film, whereby a moiré phenomenon can be prevented from occurring. At this time, peak and valley portions of the optical patterns 2-1 may have different heights t1 and t2 and different depths D1 and D2 due to the irregular pitches, respectively.
An optical film 3 disclosed in Korean Laid-open Patent Publication No. 10-2007-0084410 is shown in FIG. 3. Prism patterns 3-1 formed on a surface of the optical film 3 shown in FIG. 3 have winding shapes, whereby a moiré phenomenon is prevented from occurring.
Among these conventional optical films, in case of the optical film 1 disclosed in U.S. Pat. No. 6,354,709, valley portions of the optical patterns 1-1 are linearly arranged except that the peak portions are non-linearly arranged, and the other optical structures are regular, which include the height of the peak portion, the depth of the valley portion, an angle and the like of each optical pattern 1-1. For this reason, such regular structural elements may cause a moiréphenomenon.
Particularly, both optical surfaces (i.e., surfaces formed from a peak portion to valley portions) of each optical pattern are symmetric as the optical surfaces are close to the valley regions. Consequently, such a structure causes a moiré phenomenon.
Further, in the optical film 2 disclosed in U.S. Pat. No. 5,919,551, the optical structure in which the optical patterns 2-1 are linearly arranged causes a moiré phenomenon.